Manufacture of electrochemical sensors by screen-printing is known (Czech patent 291411) and allows a cheap and effective manufacture of electrochemical sensors and biosensors. The principle of the manufacture of the working electrodes of such electrochemical sensors lies in applying pastes containing active materials by screen-printing. The active material (mostly gold, platinum, silver) is dispersed as very fine particles in a carrier, which ensures that the material is in the form of paste. This paste is applied to a suitable pad by means of printing. The paste is then hardened, optionally fired, which creates the active layer of the sensor, or the vehiculum of paste is evaporated and the active layer of the working electrode of the electrochemical sensor is then created by sintering. The disadvantage of this method is not only the porousness and the complexity of the surface structure of the printed layer, but also the fact that the carrier material can strongly influence the detection properties of the electrode. The final functional properties of the working electrode are determined by hardening of the binder or by sintering the paste particles. In all cases, the relief of the particles is transferred into the topography of the surface of the working electrode. However, in some cases the quality of the surface is crucial for the final application of the electrode.
The method of the preparation of the working electrode as described above is advantageous in the applications in which a large area of the working electrode of the sensor is needed. However, in many applications the porousness and the complexity of the surface structure of the printed layer is disadvantageous, especially when the surface of the working electrode is modified with bioactive substances such as antibodies or DNA segments. In case of DNA segments the inhomogeneities of the surface directly influence the reproducibility of the hybridization process. A further disadvantage of the working electrodes with a complex surface structure is the fact that in some cases the immobilized biochemical layer can distinctively inhibit the mass transfer between the environment, the bioactive layer of the sensor on the working electrode and the working electrode itself.
Several methods of enhancing the structure of the electrode are known in the art. One of them is described in EP 1300897, where a more homogenous nanostructure is obtained by insertion of a nanoporous ceramic element. Another possibility is imprinting of suitable matrix, which brings the nanostructure on the electrode. EP 1342736 describes this method and suitable materials. A process of controlled sintering of the electrode from nanoparticles is described in EP 1244168 and EP 1207572. Another possibility is to apply a suitable material, which creates the required nanostructure on the surface of the electrode (mentioned in U.S. Pat. No. 6,060,121) by further technological process. Another method of enhancing the properties of the working electrode lies in the use of nanostructured filler, from which the working electrode is composed, as described in WO 98/56854. Further processes of transferring the nanostructures to the working electrode are described in U.S. Pat. No. 2004/241896 and WO 2004/052489. The processes enhancing the properties of the working electrodes as described above have also some disadvantages. However, these processes do not bring on the solution for preparing extremely homogeneous structure of the electrode surface. These methodics are expensive and it is difficult to transfer them into a mass production.
Another essential problem of the existing method of manufacturing of the working electrodes by screen-printing is that the number of materials that can be treated by the screen-printing method (i.e. as particles in a paste) is limited. There are many materials that are nanostructured—i.e. materials having periodic structures with a characteristic measure smaller than 1 μm. Electrodes in the shape of fields of pyramids having the baseline of 100 nm (CVD diamond anisotropic film as electrode for electrochemical sensing, K. L. Soh, W. P. Kang, J. L. Davidson, Y. M. Wong, A. Wisitsora-at, G. Swain, D. E. Cliffel, Sensors and Actuators B 91, 2003, 39-45). Most of these materials can be prepared only in the form of a film or very small objects that cannot be incorporated as working electrodes into the sensors by using the known technologies. Many other methods for the preparation of nanostructured materials in the form of films are known. EP 1443091 describes chemical processes and compounds enabling the preparation of nanostructured films. Various methods of the preparation of nanostructured films are described in US2002/106447, WO 99/35312, WO 01/27690, U.S. Pat. No. 6,301,038 and WO 2004/011672.
The purpose of the present invention is to overcome the disadvantages of the techniques known in the art.